A chip resistor is mainly constituted by a cuboid-shaped insulating substrate, a pair of front electrodes, a pair of back electrodes, end surface electrodes, a resistor, a protective layer, etc. The pair of front electrodes are disposed on a front surface of the insulating substrate and face each other with a predetermined interval therebetween. The pair of back electrodes are disposed on a back surface of the insulating substrate and face each other with a predetermined interval therebetween. The end surface electrodes bridge the front electrodes and the back electrodes respectively. The resistor bridges the front electrodes paired with each other. The protective layer covers the resistor.
Generally, such a chip resistor is produced in the following manner. That is, electrodes, resistors, protective layers, etc. as many as a large number of chip resistors are formed collectively on a large-sized aggregate substrate. Then, the aggregate substrate is divided along division lines (e.g. division grooves) arranged into a latticed pattern so that the large number of chip resistors can be obtained. In such a chip resistor producing process, a resistive paste is printed and sintered on one surface of the aggregate substrate to thereby form the large number of the resistors. However, due to the influence of positional displacement or blurring during the printing or temperature unevenness in a sintering furnace etc., it is difficult to avoid generation of some variation in size or film thickness among the resistors. For this reason, it is necessary to perform resistance value adjustment work for forming a trimming groove in each resistor in the state of the aggregate substrate so as to set a resistance value of the resistor at a desired one. The trimming groove is a slit formed by irradiation with laser light. As to the shape of the slit, a trimming method called “L-cutting” or “straight cutting” is the mainstream. However, a chip resistor using a trimming method called “scanning and cutting” in order to obtain a resistance value with ultrahigh precision has been also proposed (e.g. see Patent Literature 1).
FIG. 5 is a plan view of a chip resistor 10 disclosed in the aforementioned Patent Literature 1. The chip resistor 10 is provided with a pair of front electrodes 12, a resistor 13, etc. The pair of front electrodes 12 are disposed on an insulating substrate 11 and face each other with a predetermined interval therebetween. The resistor 13 shaped like a rectangle bridges the front electrodes 12. An inverted U-shaped trimming groove 14 is formed in the resistor 13. A resistance value of the chip resistor 10 is regulated by the resistor 13 in which the trimming groove 14 has been formed. By the trimming groove 14, the resistor 13 is divided into two, i.e. a body portion 13a and a cut-out portion 13b. A procedure for forming the trimming groove 14 having such a shape will be described below based on FIG. 6.
First, as shown in FIG. 6(a), a place (start point) S1 at a distance from the resistor 13 on the insulating substrate 11 is irradiated with laser light, while measurement terminals (probes) are brought into contact with the pair of front electrodes 12 to measure a resistance value of the resistor 13. On this occasion, the start point S1 is set at a place slightly distant from the resistor 13, for example, an intermediate portion (on a division line in FIG. 6) between the resistor 13 and another adjacent resistor 13 in order to prevent the resistor 13 from being damaged unwillingly due to positional displacement. As shown in FIG. 6(b), the place irradiated with the laser light is scanned right upward in FIG. 6(b) from the start point S1 toward one side surface of the resistor 13. Then, as shown in FIG. 6(c), the place irradiated with the laser light is extended to the inside of the resistor 13 as it is. Thus, a slit 15 shaped like a straight line perpendicular to a current direction is formed. The resistance value of the resistor 13 increases gradually due to the slit 15. After the resistance value is increased until the measured resistance value is lower than a target resistance value by a certain degree, the direction of the slit 15 is changed by 90° C. at a first turning point T1 so that the slit 15 can be extended in a parallel direction to the current direction, as shown in FIG. 6(d). Thus, the resistance value is further increased. Then, as shown in FIG. 6(e), the direction of the slit 15 is changed by 90° at a second turning point T2 and moved downward to thereby form an inverted U-shaped trimming grove 14. Thus, the resistor 13 is divided into two, i.e. a body portion 13a and a cut-out portion 13b. At this point of time, the resistance value of the resistor 13 is adjusted to a value (about −1% to −5%) slightly lower than the target resistance value. Next, laser light is applied to the body portion 13a side of the trimming groove 14 to gradually cut (scan and cut) the body portion 13a, as shown in FIG. 6(f). Thus, the resistance value of the resistor 13 is adjusted relatively to the target resistance value with extremely high precision.
According to such a trimming method, the cut-out portion 13b trimmed into an inverted U-shape is provided in a portion of the resistor 13 to thereby roughly adjust the resistance value. Therefore, a time required for the rough adjustment of the resistance value can be shortened. In addition, the inverted U-shaped slit is scanned and cut gradually linearly to be widened. Thus, the roughly adjusted resistance value is finely adjusted. Accordingly, the resistance value of the resistor 13 can be adjusted rapidly and precisely.